Because copper atoms diffuse rapidly into other materials, such as dielectric materials, conductors made of copper or copper alloy in a semiconductor device are surrounded with diffusion barriers. Prior diffusion barriers were formed by etching trenches or vias in a dielectric layer, and then sputtering, evaporating, or chemical vapor depositing a metallic diffusion barrier material onto the surfaces of the layer. Sputtering and evaporating techniques, however, did not produce diffusion barriers which conformed to the surfaces of the dielectric layer. The nonconformal coverage created "weak points" in the diffusion barriers at the bottom edges of the trenches or vias where copper atoms could diffuse through into the dielectric layer. Although chemical vapor deposition provided conformal coverage over the dielectric layer, the metallic diffusion barriers produced by this technique included many grain boundaries which could act as rapid diffusion paths for copper atoms. Consequently, metallic diffusion barriers deposited by chemical vapor deposition became increasingly unreliable at thin thicknesses. Furthermore, ultra-thin (i.e., less than 10 nm) diffusion barriers, which are required for deep submicron low-resistance copper interconnects, were difficult to produce in a controllable manner by any of the above-described techniques.